| /* |
| * Licensed to the Apache Software Foundation (ASF) under one or more contributor license |
| * agreements. See the NOTICE file distributed with this work for additional information regarding |
| * copyright ownership. The ASF licenses this file to You under the Apache License, Version 2.0 (the |
| * "License"); you may not use this file except in compliance with the License. You may obtain a |
| * copy of the License at |
| * |
| * http://www.apache.org/licenses/LICENSE-2.0 |
| * |
| * Unless required by applicable law or agreed to in writing, software distributed under the License |
| * is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express |
| * or implied. See the License for the specific language governing permissions and limitations under |
| * the License. |
| */ |
| package org.apache.geode.cache.query.internal; |
| |
| import org.apache.geode.annotations.Immutable; |
| import org.apache.geode.annotations.internal.MakeNotStatic; |
| |
| /** |
| * This class is intended to hold a single 'observer' which will receive callbacks from the query |
| * subsystem when various events take place. There can be only one such observer at a time. If no |
| * observer is needed, this member variable should point to an object with 'do-nothing' methods, |
| * such as QueryObserverAdapter. |
| * |
| * Code which wishes to observe events during a query should do so using the following technique: |
| * |
| * class MyQueryObserver extends QueryObserverAdapter { // ... override methods of interest ... } |
| * |
| * QueryObserver old = QueryObserverHolder.setInstance(new MyQueryObserver()); try { //... call |
| * query methods here ... } finally { // reset to the original QueryObserver. |
| * QueryObserverHolder.setInstance(old); } |
| * |
| * The query code will call methods on this static member using the following technique: |
| * |
| * QueryObserver observer = QueryObserverHolder.getInstance(); try { |
| * observer.startMethod(arguments); doSomething(); } finally { observer.stopMethod(arguments); } |
| * |
| * @version $Revision: 1.1 $ |
| */ |
| public class QueryObserverHolder { |
| |
| /** |
| * The default 'do-nothing' query observer * |
| */ |
| @Immutable |
| private static final QueryObserver NO_OBSERVER = new QueryObserverAdapter(); |
| /** |
| * The current observer which will be notified of all query events. |
| */ |
| @MakeNotStatic |
| private static QueryObserver _instance = NO_OBSERVER; |
| |
| /** |
| * Set the given observer to be notified of query events. Returns the current observer. |
| */ |
| public static QueryObserver setInstance(QueryObserver observer) { |
| Support.assertArg(observer != null, "setInstance expects a non-null argument!"); |
| QueryObserver oldObserver = _instance; |
| _instance = observer; |
| return oldObserver; |
| } |
| |
| public static boolean hasObserver() { |
| return _instance != NO_OBSERVER; |
| } |
| |
| /** Return the current QueryObserver instance */ |
| public static QueryObserver getInstance() { |
| return _instance; |
| } |
| |
| /** |
| * Only for test purposes. |
| */ |
| public static void reset() { |
| _instance = NO_OBSERVER; |
| } |
| } |